feat(audio): ffmpeg production pass — loop/loudnorm builders, runner, build script

Pure arg builders (audio_ops) + thin runner (audio_run) + build_audio_media.py.
Produces the 5 normalized soundtrack loops + a synthesized pink-noise bed under
the gitignored sample_media/audio tree. 6 tests pass (white-noise integration
runs against bundled imageio_ffmpeg).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

simulator/build_audio_media.py

@@ -0,0 +1,43 @@
+"""Production pass for the 5 per-altitude soundtracks + the white-noise bed
+(audio spec §5.3). The audio analogue of build_pool_manifest.py --media: read the
+sourced ambience clips (re-downloadable per docs/audio-candidate-pool.md), make
+each a seamless loudness-normalized loop, and synthesize the pink-noise bed.
+
+Media is gitignored; this script is the reproducible record. Outputs land under
+simulator/sample_media/audio/<scale>/<name>.loop.mp3 and audio/noise/pink.mp3,
+served at /media/audio/...  Run:  python simulator/build_audio_media.py
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from tools.pipeline.audio_run import generate_white_noise, process_soundtrack
+
+AUDIO = Path(__file__).parent / "sample_media" / "audio"
+
+# scale -> (sourced raw file, production output file), both under audio/<scale>/.
+# Sources per docs/audio-candidate-pool.md (the "✓ KEEP" picks).
+SOURCES: dict[str, tuple[str, str]] = {
+    "cosmos": ("pillars.mp3", "pillars.loop.mp3"),
+    "orbit": ("spaceamb.mp3", "spaceamb.loop.mp3"),
+    "coast": ("waves.mp3", "waves.loop.mp3"),
+    "reef": ("soundscape.mp3", "soundscape.loop.mp3"),
+    "abyss": ("whale.wav", "whale.loop.mp3"),
+}
+
+
+def main() -> None:
+    for scale, (raw, out) in SOURCES.items():
+        src = AUDIO / scale / raw
+        if not src.exists():
+            print(f"  SKIP {scale}: source missing ({src}) — re-source per audio-candidate-pool.md")
+            continue
+        dst = process_soundtrack(src, AUDIO / scale / out)
+        print(f"  produced {dst.relative_to(AUDIO.parent)}")
+    noise = generate_white_noise(AUDIO / "noise" / "pink.mp3")
+    print(f"  produced {noise.relative_to(AUDIO.parent)}")
+
+
+if __name__ == "__main__":
+    main()